Ask
students to explain what they know about global warming and global dimming.
Review these climate phenomena with students, including how the phenomena are
believed to occur and what their effects may be. (See Background for
more information.)

Organize students into three groups to take notes on the following topics as
they watch the program: the possible causes of global dimming, the evidence
that global dimming occurs, and the tools and techniques used to study global
dimming.

After Watching

Have groups present their notes. Why does global dimming occur only
during the daylight hours, while global warming occurs both during day and
night? How is global dimming causing scientists to re-evaluate current climate
models? (Because global dimming seems to have been reducing the global
temperature, the actual effect of global warming may be much stronger than
predicted by current models.) Based on evidence presented in the program,
what is the confidence level among students concerning current and future
models of global dimming and global warming? Have students defend their
reasoning.

Ask students what can be done to reduce global dimming. (The particulate
pollutants that block infrared and visible light can be reduced.) Should
these steps be taken without also addressing global warming? Why or why not?
(No, it seems most important to lessen both effects. Decreasing global dimming
may increase the impact of global warming.) If what is depicted in the
program is true, what steps would students be willing to take to reduce global
dimming? Global warming?